There exist two commonly implemented front-end architectures in radio frequency (RF) receiver design; namely, the homodyne architecture and the heterodyne architecture. The homodyne architecture down-converts a desired channel directly from RF to baseband, whereas the heterodyne architecture down-converts a desired channel to one or more intermediate frequencies (IF) before down-conversion to baseband. In general, each of these front-end architectures employ an antenna or cable to receive an RF signal, a band-pass filter to suppress out-of-band interferers in the received RF signal, a low noise amplifier (LNA) to provide gain to the filtered RF signal, and one or more down-conversion stages.
There are several competing performance goals in the design of RF receiver front-ends, including high-gain, high-linearity, low-power, and low-noise. For example, in one commonly implemented RF receiver front-end, an additional transconductance amplifier immediately follows the LNA to provide additional gain and to convert a received RF signal from a voltage to a current. Although the transconductance amplifier provides higher-gain, the additional gain comes at the cost of reduced linearity of the amplified signal. Moreover, to ensure low-noise contribution by the transconductance stage, more power has to be expended.
In another commonly implemented RF receiver front-end, a received signal strength indicator (RSSI) module can be used in conjunction with a programmable gain LNA to improve linearity. Based on the signal strength output from the LNA, the RSSI module can adapt the gain of the LNA accordingly. For example, when an adjacent blocker is present near the desired frequency portion of an RF signal, the LNA output can be quiet large and, as a result, non-linear. The RSSI module can measure the strength of this signal, and reduce the gain of the LNA to improve its output linearity. However, the RSSI module typically does not allow for a single-chip RF receiver front-end solution, leading to increased cost. In addition, as an off-chip component, the RSSI module degrades the overall noise figure performance of the RF receiver front-end.
Therefore, what is needed is an RF receiver front-end that can provide comparatively higher-gain, higher-linearity, lower-noise, and lower-power than traditional architectures.
The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.